Headworks:

Wastewater enters the treatment plant through the headworks,
which consists of mechanical screens, screening washer compactors,
and grit chambers.

Material caught by the mechanical screens is removed, cleaned
and dewatered before disposal.

The grit chambers remove grit by inducing a vortex pattern
in the circular chamber. A drive paddle in the vortex unit
maintains circulation under all flow conditions. Grit slurry
pumps periodically remove the accumulated grit from the hopper
at the bottom of the grit chambers. The grit is dewatered
before being removed to disposal bins.

Primary Treatment:

Suspended solids (sludge) settle at the bottom of the primary
tanks and are swept gently to collection hoppers to be pumped
away and processed. Surface skimmers remove floating debris
(scum). The sludge and scum are pumped to the Biosolids facility
for treatment and disposal. The remaining water (effluent)
flows by gravity to aeration tanks for secondary treatment.

Nutrient Removal and Aeration Tanks:

The conventional activated sludge process involves nutrient
(phosphorus) removal from the wastewater, aeration using micro-organisms
to consume waste, and clarification to settle micro-organisms.

Nutrient (Phosphorus) Removal: As the wastewater enters
the aeration tank, ferrous chloride is added to remove phosphorus.
The ferrous chloride makes the phosphorus in the wastewater
settle to the bottom in the final clarifiers.

Aeration (Feeding the Micro-organisms): Large, dense
populations of bacteria, protozoa, and other micro-organisms
consume suspended and dissolved organic matter. As they need
oxygen to live, air is pumped through diffusers in the base
of the tanks. The rising bubbles of air also provide a mixing
action, keeping the micro-organisms suspended and in contact
with the wastewater.

Secondary Clarifier:

The wastewater, along with the micro-organisms, flows into
secondary clarifiers. Activated sludge is settled and collected
at the base of the clarifiers. A portion of the activated
sludge (RAS) is pumped back to the influent end of the aeration
tanks. The remainder of the activated sludge (WAS) is pumped
to the WAS tanks in the biosolids building.

Final Outfall:

Secondary-treated effluent flows over the clarifier weirs. Sodium
hypochlorite is added at the beginning of the outfall for disinfection.
Sodium bisulphate is added towards the end of the outfall for dechlorination.

The final effluent is discharged to Lake Ontario through a pipe
reaching 1,250 metres offshore to a diffuser. This structure ensures
the effluent is retained for long enough to be thoroughly disinfected.
The 35 separate ports in this 188 metre-long pipe discharge the
final effluent over a large area to minimalize environmental impact.